The present invention is related generally to internal combustion engines, and, more particularly, to an inter-cylinder lubrication system for a two-cycle internal combustion engine.
In certain known internal combustion engines, a cylinder block can be arranged with two banks of vertically-stacked cylinders. In a six-cylinder engine, for example, each cylinder bank has three cylinders. Each cylinder includes a sleeve and a piston which moves relative to the sleeve between top dead center and bottom dead center positions. It will be appreciated that the foregoing terminology of top dead center and bottom dead center is used for the sake of traditional usage and is not meant to describe the piston/cylinder geometry in engines having vertically-stacked cylinders since the reciprocating motion of the piston occurs along a generally horizontal axis as opposed to the more traditionally oriented vertical axis. As indicated from the traditional “top dead center” and “bottom dead center” terminology, more often than not, internal combustion engines are orientated horizontally with respect to the crankshaft such that the pistons and cylinders are arranged generally in the vertical. Granted, in “V” engines, each piston and cylinder assembly is not perfectly vertical, but it is well known that the center of the “V” is generally arranged in the vertical. However, there are many applications that require the engine to be mounted in the vertical. That is, the crankshaft orientation is in the vertical, and the piston-cylinder arrangements assemblies are orientated generally in the horizontal. Such applications can include outboard motors, personal watercraft, lawn and garden equipment, snowmobiles, etc.
In a typical two-stroke engine, there is no oil sump to lubricate the internal components of the engine. Therefore, oil is either mixed with the fuel prior to being drawn into the engine, or is injected directly into the crankcase area to provide the necessary lubrication. In a typical crankcase-scavenged two-stroke engine, whether it be carbureted or fuel injected, crankcase fluid is moved from the crankcase to the combustion chamber through at least one transfer passage which connects the crankcase to the combustion chamber and wherein the piston acts as a valve opening and closing the ports to and from the transfer passage. The crankcase fluid consists of gasoline, air, and oil for typical carbureted and port fuel injected engines, and air and oil in typical direct fuel injected (DFI) engines. During engine operation of a vertically oriented two-stroke crankcase-scavenged engine, oil from the crankcase fluid tends to separate from the other constituents and gather in the lower portions of the crankcase and transfer passage, as influenced by gravity. This separated oil is then directionally influenced to move from the crankcase to the combustion chamber by the motion of the crankcase fluid as it moves from the crankcase to the combustion chamber through the transfer passage. Once the oil reaches the transfer passage, its duty as a lubricant is mostly complete. In such prior art engines, this excess lubricant is drawn into the combustion chamber with the crankcase fluid and is consumed in the combustion process. This leads to increased pollutants exhausted from the engine and inefficient use of oil.
Therefore, it would be desirable to design a lubrication system that prevents entry of excess oil into the combustion chamber thereby limiting the output pollutants of the engine and makes more efficient use of lubricating oil within the engine. In this regard, it would be desirable to provide a lubrication system for a non-horizontally arranged engine that re-circulates lubricant downwardly from one crankcase chamber to a next and provide a re-circulation loop to reuse the lubricating oil and not simply burn it in the combustion chamber when its initial function is complete in each cylinder.